1. Field of the Invention
The present invention relates generally to asynchronous transfer mode (ATM) communications networks, and more specifically to a source routing technique using quality-of-service parameters as a determining factor for establishing a connection through ATM network nodes.
2. Description of the Related Art
A number of proposals have hitherto been made for dealing with the problem of source routing in a connection-oriented network such as ATM network An optimum path is selected from a number of possible paths by checking a user-specified quality-of-service (QOS) parameter against resource constraints of the links of each possible path. The QOS parameters are resource constraints such as transmission delay time, delay time variation, transmission error rate and cell loss rate. In response to a connection request from a user terminal, each node of the network makes a search through possible paths stored in a topology database and selects an optimum path that satisfies one of QOS parameters specified by the connection request. Known source routing algorithms involve a significant amount of on-demand computations to check to see if all of the user-specified QOS constraints are satisfied by the links of all possible paths. This will result in a long call establishment delay.
The topology database is updated at periodic intervals to adapt to changing conditions of the network. However, since the database does not precisely represent the network conditions on a real-time basis, the call establishment delay will produce instances where calls encounter discrepancies between what is expected at the source and what is actually available in the intended path, resulting in unsuccessful call attemps.